1. Field of the Invention
The present invention relates to direct current (DC) solid state series wound motor drives for hoist and crane applications.
2. Description of Related Art
Series wound motors on hoists have been controlled with contactor resistor controls. Such arrangements are a maintenance problem and very energy inefficient. Moreover, they have the problem of not being able to provide high torque at low speed because the speed limiting resistors also limit current into the motor, and they can only provide the same value of current to the motor that is drawn from the supply.
Power distribution collector bars to the cranes are by necessity of heavy construction and the power supply has to be capable of providing very high currents when accelerating heavy loads. These heavy currents are transmitted to the crane by collector brushes, which are a maintenance item. The series motor can be abused by such systems. If the motor is overloaded and all the control resistors are shorted off, then full stall current can be applied to the motor. The hoist has to be protected from being pulled into its own mechanism, thus stalling the motor and full stall torque causing the cable to break and drop the load.
A second existing method of control is by AC/DC conversion (phase control) which can provide a stepless control; but it too has severe torque limits at low speed, must have an AC supply and does not provide significant current amplification.
U.S. Pat. No. 3,289,063, issued on Nov. 29, 1966 to Brooks H. Short, describes a series motor having parallel connected transistors that control the current flow through the field of the series motors such that the field winding is divided into smaller segments which are connected respectively in series with the transistors. Short does not suggest the DC solid state series wound motor drive according to the claimed invention.
U.S. Pat. No. 3,346,771, issued on Oct. 10, 1967 to Robert S. Sutton, describes a digital electronic speed control governor which is designed to hold the speed of an internal combustion engine at 3600 r.p.m. plus or minus 10 r.p.m., between full load and no load conditions, so that the generator connected to the engine output and operating at a frequency of 60 cycles per second at 120 volts would maintain this frequency within one cycle per second and the voltage within 2 volts. Sutton does not suggest the DC solid state series wound motor drive according to the claimed invention.
U.S. Pat. No. 3,535,605, issued on Oct. 20, 1970 to John A. Halvorson et al., describes a static reversing chopper shunt motor hoist control system with a limit stop and a backout control means operable in combination therewith for applying dynamic braking and mechanical braking to stop a load, for reversing the mechanical brake and for providing reduced negative torque to drive the load down in response to lowering operation, and for limiting the backout speed at both no load and full load conditions in the event the limit stop and backout control means do not reset. Halvorson et al. do not suggest the DC solid state series wound motor drive according to the claimed invention.
U.S. Pat. No. 3,548,279, issued on Dec. 15, 1970 to Max S. Knasinski et al., describes a static control system for a shunt motor having an armature winding and a shunt field winding to provide an improved voltage bootstrap circuit for lowering the control voltage on a gating type switching circuit as soon as it is fired into conduction, thereby minimizing the firing circuit power requirements for a plurality thereof connected to the same voltage supply. Knasinski et al. do not suggest the DC solid state series wound motor drive according to the claimed invention.
U.S. Pat. No. 3,551,771, issued on Dec. 29, 1970 to Robert L. Risberg et al., describes a static control system for the shunt motor field of a crane hoist having a static field supply and a solid state reversing chopper supplied from a constant potential bus for armature control with a first semiconductor controlled rectifier (SCR) controlled resistor loop for 75 percent second quadrant retarding torque and a second SCR controlled resistor loop usable with the first one for 150 percent fourth quadrant retarding torque. The Risberg et al. '771 patent does not suggest the DC solid state series wound motor drive according to the claimed invention.
U.S. Pat. No. 3,553,554, issued on Jan. 5, 1971 to Robert L. Risberg, describes a constant potential bus static reversing chopper hoist static shunt motor control system with improved means for providing control retarding torque upon the hoist, which is controllable from zero to a first value limit, and for providing additional retarding torque upon lowering that is controllable from a zero to a larger value. The Risberg '554 patent does not suggest the DC solid state series wound motor drive according to the claimed invention.
U.S. Pat. No. 3,555,384, issued on Jan. 12, 1971 to John A. Halvorson et al., describes a static, constant potential bus, shunt motor control system having a static chopper circuit with means serving the dual function of protecting the switching devices from excessive supply voltage and decaying the commutating energy after it has performed its function. Halvorson et al. do not suggest the DC solid state series wound motor drive according to the claimed invention.
U.S. Pat. No. 3,555,385, issued on Jan. 12, 1971 to Robert L. Risberg, describes a static, constant potential bus, shunt motor control system having smooth regenerative braking control means with static anti-plugging control means. The Risberg '385 patent does not suggest the DC solid state series wound motor drive according to the claimed invention.
U.S. Pat. No. 3,746,954, issued on Jul. 17, 1973 to Asa H. Myles et al., describes a hoist control system for operating a direct current series motor from a single-phase or three-phase alternating current source. Myles et al. do not suggest the DC solid state series wound motor drive according to the claimed invention.
U.S. Pat. No. 4,385,266, issued on May 24, 1983 to Albert E. Sloan, describes a pulse control circuit for a DC series motor which has an armature and two oppositely-wound field windings, that includes two semiconductor static switching devices, such as thyristors. The control means is adapted, when the mark-to-space ratio of one of the static switching devices has been brought to a predetermined maximum value, to cause simultaneous operation of the other static switching device at a lower mark-to-space ratio thereby energizing the associated field winding so as to reduce the net flux in the motor and further increase the motor speed. Sloan does not suggest the DC solid state series wound motor drive according to the claimed invention.
U.S. Pat. No. 4,506,200, issued on Mar. 19, 1985 to Walter Datwyler et al., describes a control system for operating a shunt wound DC motor by controlling the motor to follow the operating characteristics of a conventional shunt wound motor when this characteristic is optimal and to follow alternatively the operating characteristics of a conventional series wound motor when this second characteristic is optimal. Datwyler et al. do not suggest the DC solid state series wound motor drive according to the claimed invention.
U.S. Pat. No. 4,639,647, issued on Jan. 27, 1987 to Bonne W. Posma, describes a controller for controlling at least one series motor that includes connecting rectifier means in series with the motor such that the current to the field winding of the motor is always in the same direction irrespective of the plurality of the input voltage. Further, the controller provides for applying an energizing current to the field winding to ensure that the field winding always produces some flux during operation of the motor such that a counter EMF always exists whenever the motor rotates. Posma does not suggest the DC solid state series wound motor drive according to the claimed invention.
U.S. Pat. No. 4,677,356, issued on Jun. 30, 1987 to Haruhiro Tsuneda et al., describes a drive motor device that detects and measures the level of the motor drive current, and when the drive control device detects that the motor drive current exceeds a predetermined target value, a gating circuit in the path of the forward and reverse drive signals is directed to invert the forward and reverse drive signals thereby reversing the direction of the motor direction drive current. This results in a braking action. Tsuneda et al. do not suggest the DC solid state series wound motor drive according to the claimed invention.
U.S. Pat. No. 5,274,541, issued on Dec. 28, 1993 to Shin Kimura et al., describes that in a module using a high speed switching element, such as an insulated gate bipolar transistor (IGBT), for a high speed inverter, a matching condition is established between the switching characteristic of the IGBT and the recovery characteristic of a diode connected thereto in an antiparallel fashion. The oscillating voltage appearing in the inverter circuit, as a result of the IGBT, is suppressed to prevent erroneous operation of the inverter system. Kimura et al. do not suggest the DC solid state series wound motor drive according to the claimed invention.
U.S. Pat. No. 5,332,954, issued on Jul. 26, 1994 to Robert Lankin, describes an electric controller for a motor that has an H-bridge circuit for controlling a field current of the motor. The controller may be configured with a series wound or a separately excited DC traction motor. Lankin does not suggest the DC solid state series wound motor drive according to the claimed invention.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed.